This invention relates generally to analyzing imbalance of rotating vehicle wheel, and in particular to calibrating wheel balancer apparatus and analyzing wheel/tire imbalance to determine the magnitude and angular location of corrective counter-balance mass(es) to be be placed on the wheel rim(s).
The determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by the imbalances, and noise.
It is necessary to calibrate each wheel balancer to take into account manufacturing variations in the components, such as the spindle on which the wheel/tire assembly is mounted, the sensor/transducers, and the electronic circuitry, for example. Moreover, considerable expense has been incurred in connection with prior art balancers to obtain precision parts to limit as much as possible the balancer-to-balancer variation.
Heretofore, accuracy in wheel balancing was also affected by the requirement that the precise geometrical relationship of the sensors to the wheel be known in order to accurately calculate imbalance. Changes in the sensor spacing, for example, or loose tolerances with respect to the geometry, could result in considerable errors in the resulting wheel imbalance measurement made by prior wheel balancers. The requirement of producing balancers with precise geometrical relationship of the sensors to the wheel results in high manufacturing costs, poor performance, and greater maintenance.
Even when calibrated properly and with precision components, prior art wheel balancers are not as accurate as they could be. Existing balancers for the most part use various models of the balancer structure to make a first estimate of wheel/tire imbalance and accept that first estimate as the actual imbalance. If the construction of the balancer does not match the requirements of the model, considerable inaccuracies in measurement of imbalance results. In fact, these first estimates of wheel/tire imbalance can be substantially improved.
In addition, the imbalance measurements obtained using existing wheel balancers are not as reproducible as could be desired.